Device for sensing the product of the density and the square of the rate of circulation of a fluid



NOV. 24, 1970 M, R, JONES ETAL 3,541,854

DEVICE FOR sENsING THE PRODUCT 0F THE DENSITY AND THE SQUARE 0F THE RATE0F CIRCULATION CF A FLUIL Original Filed Dec. 30, 1966 3 Sheets-Sheet IIk 44a/wn i. (fo/76u Nov. 24, 1970 M, R JONES ETAL 3,541,854

' DEVICE FOR SENSING THE PRODUCT OF THE DENSITY AND THE SQUARE OF THERATE OF CIRCULATION OF A FLUID Original Filed Dec. 50, 1966 3Sheets-*Sheet 2 l N VEN TORJ mh, .mq NE N mv.. Nw

nvm. Se mb S DSN 4 N i 5 Sheets-Sheet I5 M. R. JONES ETAI- Nov. 24, 1970DEVICE FOR SENSING THE PRODUCT vOF THE DENSITY AND THE SQUARE OF THERATE OF CIRCULATION OF A FLUID Original Filed Deo.

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United States Patent Olce 3,541,854 Patented Nov. 24, 1970 3,541,854DEVICE FOR SENSIN G THE PRODUCT F THE DENSITY AND THE SQUARE 0F THE RATEOF CIRCULATION 0F A FLUID Marvin R. Jones and Benton F. Baugh, Houston,Tex., assignors to Cameron Iron Works, Inc., Houston, Tex. Originalapplication Dec. 30, 1966, Ser. No. 606,312, now Patent No. V3,429,385.Divided and this application July 3, 1968, Ser. No. 742,386

Int. Cl. G01f l/06 U..S. Cl. 73-228 3 Claims ABSTRACT 0F THE DISCLOSUREA choke is connected to an outlet from the upper end of the annulusbetween a well bore penetrating an earth formation containing fluidunder pressure and a drill string extending into the well bore. When akick is encountered during drilling of the well, a blowout preventer atthe wellhead about the outlet may 'be closed to divert drilling fluidcirculating through the drill string and annulus through the choke. Thechoke is responsive to a bias and a control signal for regulating thepressure of the drilling fluid in order to maintain the differentialbetween the bottom hole pressure of such drilling fluid and the pressureof the formation fluid at a predetermined value. Means are provided forproducing a control signal and a bias which cooperate to cause the choketo respectively increase or decrease the formation fluid pressure withinthe outlet automatically in response to a deviation, negative orpositive, from said predetermined pressure differential, whereby theoutlet pressure approaches a value at which such deviation is zero. Thebias is a signal representing the pressure of the drilling fluid withina standpipe connected to the upper end of the drill string, and thecontrol signal represents the sum of the circulating pressure losswithin the drill string, the static pressure of the drilling iluid insuch standpipe, and the predetermined pressure differential. The signalproducing means includes a device for sensing the product of the densityand the square of the rate of circulation of drilling fluid within theupper end of the drill string, which is useful in computing thecirculating pressure loss within such string. The device includes aconduit adapted to be connected in the drill string, a rotatable shaftextending through the side of the conduit, and an arm on the shaftwithin the conduit for rotation with the end extending longitudinally ofthe conduit. A sensing element is mounted and arranged on the end of thearm remote from the shaft for swinging out of a neutral position inproportion to MV2, wherein M equals the density and V the velocity of afluid such as drilling mud flowing through the conduit. There is a meansincluding a transmitter on the exterior of the conduitand responsive toloads of the arm due to swinging of the sensing element for returningthe sensing element to its neutral position. The transmitter has meansfor producing asignal which is a mathematical function of the forcenecessary to so return the sensing element.

This application is a division of my copending application, Ser. No.606,312, filed Dec. 30, 1966, for Well Control, now Pat. No. 3,429,385.

This invention relates to an improved device for sensing the product ofthe density and the square of the rate of circulation of drilling fluidwithin the upper end of the drill string.

In systems for use in controlling the pressure of fluid Within theannulus between a well bore and a drill string extending into the bore,it is the usual practice to provide a choke in a manifold connectingwith the annulus beneath a blowout preventer closed about the drillstring, in order to establish and maintain a back pressure in the fluiddiverted through the choke, which, together with the hydrostaticpressure of the mud, is sufficient to contain the pressure of uidswithin formations penetrated by the Well bore-ie., prevent them fromflowing into the Well bore. In the case of a kick, the choke mustcontinue to contain the formation fluid as heavier mud is circulateddown the drill string and up the annulus t0 kill the well. Moreparticularly, the choke is preferably adjustable s0 that, in controllingthe well pressure, it may be so regulated as to avoid establishingexcessive back pressure which might cause the drill string to stick, ordamage a formation, the well casing, or the wellhead equipment. In thesesystems, as distinguished from systems employing conventional positivechokes, an effort is made to so regulate the choke as to maintain aconstant bottom-hole pressure without having to change the circulatingrate.

In the use of one such system, when a kick is encountered, and with thepreventer closed, the mud pumps are stopped, the choke is closed, andshut-in pressure is observed at the manifold upstream of the choke. Thepump is then started slowly and the choke is gradually opened tomaintain a back pressure at a level slightly above the observed shut-inpressure. When the desired circulating rate is reached, it is heldconstant and the choke is continuously adjusted to maintain the pressurein a standpipe connected to the upper end of the drill string at thelevel it has reached at such circulating rate. This maintenance of aconstant pressure in the standpipe continues until the kick iscirculated out of the annulus.

The user then calculates the mud weight increase necessary to containthe formation fluid, and begins to pump the hea'vier mud into the drillstring while now adjusting the choke to maintain the annulus backpressure constant. When the heavier mud reaches bottom, the user beginsto adjust the choke in order to again maintain the drill string pressureconstant as such mud circulates up through the annulus. Thus, in effect,the user maintains a constant bottom-hole pressure by controlling thepressure in that portion of the well where the average density of thefluid in it is known more closely. This, of course, is the drill stringduring both circulation of the kick out of the annulus and circulationof heavier mud up the annulus, and the annulus when heavier mud iscirculated down the drill string.

The above-identified patent application is directed toward a system ofthis general type which is not only essen- -tially automatic in that itdoes not require manual adjustments to the choke but also enables thepractice in a variety of methods in that it does not require thecirculating rate to be maintained constant. Thus, it includes equipmentwhich automatically senses certain conditions in the well in such amanner as to enable the circulating rate to vary in the use of thesystem. The primary object 3 of this invention is to provide a devicewhich is particularly well suited for sensing one of these conditions,and more particularly for sensing the product of the density times thesquare of the circulating rate of the fluid circulating within the upperend of the drill string.

In the drawings, wherein like reference characters are used throughoutto designate like parts:

FIG. 1 is a diagrammatic illustration of such a system including asensing device constructed in accordance with the present invention andinstalled upon a typical well for controlling the pressure of sameduring drilling;

FIG. 2 is an enlarged perspective view of a console for the system, asseen from one corner thereof so as to illustrate its control panel;

FIG. 3 is a diagrammatic illustration of a pneumatic system within theconsole of FIG. 2;

FIG. 4 is a diagrammatic illustration of a portion of the pneumaticsystem of FIG. 3, with a switch thereon moved to an alternate position;

FIG. 5 is an enlarged cross sectional View of a choke in the controlsystem;

FIG. 6 is an enlarged longitudinal cross sectional view of the sensingdevice in the control system; and

FIG. 7 is another longitudinal sectional View of the sensing device, asseen along broken line 7-7 of FIG. 6.

With reference now to the details of the above-described drawings, thedrilling control system illustrated in FIG. .21 is installed upon a wellincluding a casing 20 lining a portion of a well bore 21 and a casinghead 22 connected to the upper end 0f casing 20. A blowout preventer 23connected above the casing head 22 has a bore 24 therethrough alignedwith the bore in the casing head and rams 25 mounted therein forreciprocation between extended positions for closing the bore 24 andretracted positions for opening same. More particularly, as Well knownin the art, the rams are so formed on their inner ends as to seal abouta drill string 26 extending through the preventer and into the well bore21, and thus close the annular space between the drill string andpreventer bore in order to shut the well in.

There is a bit 27 at the lower end of the drill string 26 for drillingthe well bore 21 as the string is rotated by suitable well knownapparatus located at the wellhead. A standpipe 28 is connected to theupper end of the drill string 26 above blowout preventer 23, anddrilling mud is circulated through the standpipe downwardly through thedrill string 26 to the bit 27, and upwardly within the annulus 29between the drill string and the casing 20 and uncased well bore 21.

A side outlet 30 connects with the bore of the casing head 22 beneaththe preventer 23 and above ground level G. Thus, upon closing of theblowout preventer rams 25 about the drill string, as shown in FIG. l,uid within the annulus 29 is diverted into the outlet 30. Manifolding inthe form of a cross 31 connecting with the outlet 30 provides a straightrun forming a continuation of the outlet and upper and lower wings towhich chokes 32 are connected.

The straight run, as Well as the upper and lower wings of the cross, isprovided with valves of suitable construction for selectively opening orclosing them. As shown in FIG. l, a valve in the straight run and avalve in the lower wing are closed to divert flow through the choke 32in the upper wing. In this way, the system is ready for use on the well.Alternatively, the valve in the upper wing could be closed and the valvein the lower wing opened to put the lower choke in operation. Or, whenthe system is not needed, the valve in the straight run can be openedand the wing valves closed.

As well known in the art, during the ordinary drilling of the well, thepreventer rams 25 are open so that drilling mud circulated downwardlythrough the drill string 26 and upwardly through annulus 29 passes outthe upper end of the blowout preventer 23 for collection and subsequentrecirculation through the drill string. When, howover, the well bore 21penetrates a formation F or other strata bearing uid of a higherpressure than the hydrostatic pressure of the drilling mud at anadjacent level, it has been the practice to close the preventer rams 25about the drill string to prevent the blowout of the well due to theentry of higher pressure formation fluid into the annulus. Then, aspreparations are made to replace the existing drilling mud with densermud for increasing the hydrostatic pressure in the well bore, the mudcontaining the formation fluid is diverted by the closed rams into theoutlet 30 and through a choke.

It will be understood that bottom hole pressure means the pressurewithin the 'well bore at the bottom of the drill string regardless ofthe position of the drill string in the well bore. It will also beunderstood that formation pressure at least when the drill string is notat the bottom of the well bore, is adjusted to the actual position ofthe lower end of the drill string by reducing it by the amount ofpressure due to the head of fluid between the formation and the bottomof the drill string.

As previously described, this establishes a back pressure in the annulus29 for containing formation fluid pressure. In some cases, however, whenthe choke has been of a positive type, it created a back pressure whichtended either to break down a formation or to damage the casing. Evenwhen attempts have been made to adjust the choke, the apparatus andsystems for doing so have had many shortcomings.

It is also the practice to drill a well under pressure, in which case arotating type of blowout preventer is maintained closed about the drillstring during at least a portion of the drilling of the well. In thiscase, of course, as in the case of shutting in the well upon entry offormation fluid, the drilling mud 'within the annulus would be divertedinto the owline, and through the choke 32 for imposing a back pressureon the annulus. Ths enables the operator to drill the well with at leastsomewhat lighter drilling mud.

In addition to the choke 32, the system shown in FIG. l includes aconsole 50 having computing means therein which determines and indicatescirculating pressure loss, as will be described to follow. A frontcontrol panel of the console contains various dials indicating measuredand selected values entered into the computer and knobs for settingthese values, as well as means manipulatable by the user in switchingthe system between standpipe and manifold control.

This system also has a transmitter 51 connected to the standpipe 28 andhaving a fluid line 51a leading therefrom for transmitting a signalproportional to standpipe pressure to the console 50, and particularlyto a gauge 52 on the panel having a dial thereon for indicating suchstandpipe pressure in pounds per square inch. More particularly, thereis a fluid line 53 connecting with the transmitter 51 for delivering asupply pressure thereto from an external fluid source through a line 54connecting with the console 50, and thus with the fluid line 53, bysuitable means to be described.

This system also includes a transmitter 55 connected to the side outlet30 from the annulus 29 of the well, upstream of the choke 32. A fluidline 55a therefrom transmits a signal proportional to the manifoldpressure to the console, and more particularly, to a gauge 56 on thepanel of the console having a dial for indicating such manifold pressurein pounds per square inch. This transmitter receives supply pressurethrough a fluid line 57 leading thereto from the console 50.

There is a dial 58 on the control panel for indicating the measureddepth of the well in thousands of feed, and a dial 59 adjacent to thedial 58 for indicating the calibration factor entered into the computingmeans. The value of the depth which is measured and then entered intothe computing means is adjustable by knob 58a, and the calibrationfactor is adjusted to its proper value by means of a knob 59a. Stillfurther, there is a dial 60 on the control panel for indicating thecomputed circulating pressure loss of the drilling mud in pounds persquare inch.

As indicated above, each transmitter S1 and 5S is identical and receivessupply uid from the same sourcenamely, line 54. The dial on each gauge52 and 56 has the same range, which may be, for example, -5,000 p.s.i.,for indicating signals transmitted through the lines 51a and 55a in therange of O-SO p.s.i. Thus, the signals are in the same ratio to theirrespective measured pressure.

This system further includes a device, indicated in its entirety byreference character 61, for sensing the product of the mud density timesthe square of the circulating rate. As shown and described in detail inconnection with FIGS. 6 and 7, this device comprises a conduit adaptedto be connected in the standpipe and a transmitter 62 to one side of theconduit. A signal which is a mathematical function of the product sensedthereby is transmitted by the transmitter 62 to computing means withinthe console for determining the circulating pressure loss in accordancewith the formula described below. This transmitter, similarly totransmitters 51 and 55, is connected to a fluid line 63 leading to theconsole 50 and, more particularly, to a gauge having a dial 69 on thecontrol panel of the console for indicating the product. Thistransmitter is also connected to the console by line 64 which in turn isconnected with the supply line 54 leading to the console 50.

When the signal from this sensed product is entered into the computingmeans, along with the depth of the lwell and the proper calibrationfactor, such computing means is automatically operable to compute thecirculating pressure loss in accordance with the formula:

dP=KMV2D wherein:

dPzCirculating pressure loss K=Calibration factor M=Mud density V=Mudcirculation rate D=Depth of the Well.

This computed circulating pressure loss is, as previously noted,indicated on the dial 60 on the control panel of the console 50.

It may be possible, in the use of this system, to ignore the eect of achange in well depth upon the circulating pressure loss. In this case,Well depth need not be measured and entered into the computing means ofthe console. Thus, circulating pressure loss is calculated in accordancewith the formula:

dPzKMV2 wherein:

dP=Circulating pressure loss K=Calibration factor Mf=Mud density V=Mudcirculation rate.

As illustrated diagrammatically in FIG. l, the choke 32 includes ahow-restricting member which is urged toward (to the right) and awayfrom (to the left) maximum flow-restricting position by means of anoperator 40. As will be described more fully hereinafter in connectionwith FIG. 5, the operator includes a piston sealably slidable within acylinder and connected by a stem to the flow-restricting member. Thus,uid pressure on the left-hand side of the operator piston urges themember toward maximum flow-restricting position, while uid pressure onthe opposite right-hand side thereof urges such member away from maximumflow-restricting position. For reasons to be described to follow, inthis embodiment of the choke there are equal pressure responsive areason opposite sides of the operator piston.

The opposite sides of the operator 40 for the choke 32 are connectedwith fluid lines `65 and 66 leading to the console. More particularly, asignal transmitted from the computing means through the fluid line urgesthe How-restricting member of the choke 32 to the right and thus towardmaximum How-restricting position. On the other hand, a signaltransmitted from the computing means through the uid line 66, acts uponthe right-hand side of the operator 40 so as to urge theflow-restricting member to the left and away from maximumflow-restricting position. These two signals bear the same ratio to thepressure values they represent.

As will be described to follow, the user switches the system betweenstandpipe and manifold control, by merely manipulating a lever 67 on thecontrol panel. More particularly, the user is able to swing the leverbetween an up position to place the system on standpipe control, asduring circulation of the kick out of the annulus and circulation ofheavier mud upwardly within the annulus, and a down position to placethe system on manifold control, as during circulation of the heavier muddown to the bottom of the hole. Thus, the user, merely manipulates thelever from one position to another at the proper stage in the control ofthe well.

The console 50 also has a means for producing and entering into thecomputer a signal which is a mathematical function of the sum of thestatic condition of the standpipe pressure and a selected pressure whichrepresents a desired safety margin. This includes a knob 68a adjacent adial 68 on the control panel for indicating such sum. This staticpressure is observed by the user upon stopping the mud pumps and closingthe blowout preventer rams about the drill string. The sum of staticpressure and the selected pressure is indicated on the panel and thesignal entered into the computing means, which automatically adds suchsignal to the signal which is a mathematical function of the computedcirculating pressure drop and transmits a signal proportional to theirsum through the line 65 to the left-hand side of the choke operator 40as the kick is circulated out of the annulus.

The console 50 also includes a secondary computing means for determiningthe increase in mud weight necessary to contain the well formation andfor indicating it on the dial 99 on the front panel of the console inpounds per gallon. More particularly, this secondary computing means 1sintegrated with the primary computer in that it receives and properlycombines the values entered into the primary computer for staticpressure, as indicated on dial 68, and depth of the well, as indicatedby dial 58.

As show in FIG. 3, line 51a connects standpipe transmitter 51 with thegauge having dial 52, and line 55a connects the manifold transmitter 5Swith the gauge having dial 56. As also shown in FIG. 3, the transmitterlines 51a and 55a continue beyond the gauges for connection with switchmeans in the fonm of a valve body 70 having a valve member 71 withpassageways therein switchable by means of the lever 67 between thealternate posltlons on FIG. 3 and FIG. 4. In the position of FIG. 3, oneendl of the left-hand passageway connects with the line 51a fromtransmitter 51, while in the position shown in FIG. 4, such passagewayconnects with the line 55a. The opposite end of the left-hand passagewayof valve member 71 remains connected with a uid line 72 connecting withamplifier 73 for transmitting an amplified signal from line 72 to line66 leading to the operator 40 of the choke for urging theHow-restricting member in the choke to the left and away from maximumflow-restricting position. Thus, switching of the level 67 between itsalternate positions transmits signals to the right side of the chokeoperator 40 proportional to standpipe pressure or manifold pressure, asdesired.

As also shown in FIG. 3, a fluid line 75 connecting with the indicator58 for the depth of the well leads to a force bridge 76 for transmittinga signal thereto which is a mathematical function of such depth. Anotheriluid line 77 connecting with the indicator 59 for the calibrationfactor also leads to the force bridge 76 for transmitting a signalthereto which is a mathematical function of such calibration factor.More particularly, these fluid lines are connected with regulators 91and 92 which are connected with a branch 54a of supply iiuid line 54 fortransmitting signals in a desired range. This branch supply line alsoconnects with the bridge through line 76a. In the force bridge, the twosignals are multiplied by one another, and the product is transmittedthrough fluid line 78 to a second force bridge 79.

The fluid line y63 connecting with the transmitter 62 on sensing device61 also leads to the force bridge 79 so as to transmit thereto a signalwhich is a mathematical function of the sensed product of mud densitytimes the square of the mud circulating rate. Supply fluid is alsoentered into the bridge 79 through line 79a connecting with branchsupply line 54a, and, in this bridge, the two signals transmittedthrough lines 78 and 63 are multiplied by one another. The product, asignal which is a mathematical function of the circulating pressureloss, according to the above-mentioned formula, is transmitted throughfluid line 80 to the dial 60 for indicating such loss.

A branch 80a of the fluid line 80 leads to a relay 81 to transmitthereto the signal which is a mathematical function of the circulatingpressure loss. A signal which is a mathematical function of the staticpressure indicated on dial 68 is also transmitted to the relay 81 bymeans of fluid lines 82 and 82a leading from such indicator. A line 68aalso connects line 82 with a regulator 90 which, like regulators 91 and92, is connected to branch supply line 54a. In the relay 81, the signalsare added, a constant is substracted from the sum, and the resultingsignal is transmitted through fluid line 83 leading to the valve casing70. The fluid line 82 connecting with static pressure indicator 68 alsoconnects with the valve casing 70 to one side of the connectiontherewith of fluid line 83.

Thus, upon switching of the valve member 71 by means of lever 67, theright-hand passageway may be switched between a position connecting itwith the line 82 and a position connecting it with the line 83. Theopposite end of the right-hand passageway is fixed for connection to aline 84 leading to an amplifier 85. The outlet from the amplifierconnects with line Y65 leading to the left side of the choke operator 40for transmitting a signal thereto which urges the now-restricting membertoward maximum flow-restricting position.

Thus, with the valve in the position shown in FIG. 3, the signaltransmitted through line 83 connected to lines 84 and 65 to the leftside of the operator 40' is proportional to the sum of circulatingpressure loss, as computed and indicated upon dial 60, and thepreviously measured static pressure in the standpipe plus the selectedpressure, as indicated upon the dial 68. This signal may be termed acontrol signal. At the same time, and as previously mentioned, a signalis transmitted through the line v51a connected to lines 72 and `65 tourge the How-restricting member away from maximum Iflow-restrictingposition with a signal proportional to standpipe pressure. This signalmay be termed a bias However, upon switching of the valve member 71 tothe position of FIG. 4, the signal transmitted through lines 84 and 66originates` from line 82, and is thus proportional to static pressure,while the signal transmitted through lines 72 and 66 originates fromline 55a, and is thus proportional to manifold pressure. Both thestandpipe and manifold transmitters are connected to supply line 54 bymeans of branch line 54h.

As will be understood by those skilled in the art, the above-mentionedsafety margin or selected pressure represents a predetermineddifferential between the pressure of the formation nid and the pressureof the well fluid opposite the formation uid. This pressure dif- 8ferential is a mathematical function of the standpipe pressure, thestatic pressure, and the circulating pressure loss in accordance withthe equation:

pnzfQa-ps-m wherein:

pD is the pressure differential, p1 is the standpipe pressure,

pis is the static pressure, and

p1 is the circulating pressure loss.

Upon entering the console 50, fluid supply line 54 connects with a dryer86a, a lter 86b and a pressure regu- Iator 87, all in series, and thencontinues for connection with both of the ampliers 73 and 85. Also,there are regulators 88 and 89 in each of the branch lines 54a and 54h.As previously noted, branch line 54a leads to the force bridges 76 and79, adding relay 81, line 64 connecting with the transmitter '62, forsensing elem-ent 61 and regulators 90, 91 and 92 connecting,respectively, with the indicators for static pressure, Well depth, andthe calibration factor. The other branch line 54b is connected with eachof lines 57 and 63 leading to the ilowline and standpipe transmitters,respectively.

The secondary computer for determining the mud weight necessary tobalance or underor overbalance by a predetermined pressure the formationpressure comprises a force bridge 95 adapted to divide the staticpressure times a constant by the depth of the well. For this purpose,the line 75 leading from the indicator 58 for well depth has a branchline 75a connecting with the bridge 95 for transmitting a signal theretoproportional to such depth. Also, the line 82, which transmits a signalfrom indicator 68 proportional to static pressure, has a branch 82bleading to relay 96, which adds a constant to this signal. The surnisthen transmitted as a signal from relay 96 and through line 97 to thebridge 95. Control pressure from branch 54a is also connected to each ofthe bridge 95 and relay 96.

The above-described signals alternately transmitted through line 65 tothe left-hand side of operator 40 bear the same ratio to the indicatedpressures on the control panel, and, as previously mentioned, bear a xedratio to the ratio of the signals from transmitters 51 and 55transmitted through line 66 to the right side of the operator to theactual pressure within the conduits on which they are mounted. Moreparticularly, with a choke operator 40 having equal pressure responsiveareas on its opposite sides, the pressure signals transmitted throughlines 65 and 66, respectively, bear the same ratio to the actual valuesof the measured, set or computed pressures they represent.

Thus, for example, in this system, Huid may be supplied from a suitablesource through line 54 at 80-160 p.s.i. and then reduced in theregulator 87 upstream of4 amplifiers 73 and 85 to 70 p.s.i. Regulator 88reduces the regulated supplied fluid in branch 54a from 70 p.s.i. to 20p.s.i., and regulator 89 reduces it in line 54b, which connect withlines 53 and 57, from 70 p.s.i. to 40 p.s.i.

As well known in the art, most pneumatic computer components, such asthe force bridges 76, 79 and 95 abovedescribed, operate within a rangeof 3-15 p.s.i. Thus, in this system, the signals to be entered into thecomputers are in the same range. That is, each of the dials 58indicating the depth of the well in feet, 59 indicating the calibrationfactor, and 69 indicating the sensed product of mud density times thesquare of its circulating rate is adapted to transmit a signal of 3p.s.i. at its minimum reading and a signal of l5 p.s.i. at its maximumreading. Also, the dial 60 is adapted to indicate minimum to maximumvalues for measured circulating pressure loss in response to signalsfrom the computer 79 in the same operating range.

The dial '68 for indicating observed static pressure is, on the otherhand, adapted to transmit signals in the range of -15 p.s.i. However, inthe relay 96, 3 p.s.i. is added to the signal proportional to staticpressure, and a signal proportional to the sum and in the range of 3-18p.s.i. is entered into force bridge `95. The mud weight increasecomputed in force bridge 95 is indicated on dial 99 on ascalecorresponding to the 3-15 p.s.i. range.

In the relay 81, on the other hand, this increment of 3 p.s.i. is takenfrom the signal related to the sum of cornputed circulating pressureloss and standpipe pressure. The adjusted signal, which is transmittedthrough line 83 to the switching valve, is in the range of 0-20 p.s.i.,and the scales on the dials 60 and 68 for circulating pressure loss andstatic pressure, respectively, range from 04,000 p.s.i. and 05,000p.s.i. Thus, the signal transmitted through line 83 bears the same ratioto the sum of the values indicated on these scales as does the signaltransmitted through line 82 to the value shown on the static pressurescale until the sum reaches p.s.i. as supplied to the relay. Moreparticularly, the signal in line 72 is doubled in amplifier 73, whilethe signal in line 84 is quadrupled in amplifier 85, so that theresulting signals on opposite sides of the choke ope-rator are, aspreviously mentioned, in the same ratio to the actual pressure valueswhich they represent.

In preparing to control the well with this system, and while drillingwith the well open, the user will, from time to time, adjust the knob58a for correcting the depth of well to be entered in the computer. Themud density and circulating rate need not be changed or adjusted sincetheir product, in the above-mentioned formula, is automatically sensedand entered into the computer continuously during circulation of themud. Thus, after adjusting the depth of the well setting on dial 58, theuser need only compare the standpipe pressure indicated on dial 52 withthe circulating pressure loss indicated on dial 60. If they are not inagreement, the user adjusts the knob 59a so as to change the calibratingfactor in order to bring the circulating pressure loss into agreementwith the standpipe pressure. When this is done, the user records theadjusted calibration factor which is now entered into the computer.Alternatively, and as previously described, the change in well depth maybe ignored.

The user further prepares for the kick by moving the lever 67 up tostandpipe control, which in turn moves valve member 7\1 to the right tothe position of FIG. 3. Then, when a kick is encountered, the user picksthe drill bit up off the bottom of the hole, shuts down the mud pumps,and closes the blowout preventer rams about the drill string 26. After ashort wait, he then reads the standpipe pressure on the dial 52 and themanifold pressure on the dial 56 and records both of them. He then setsthe dial 68 by means of knob 68a to indicate the static standpipepressure which he has read on dial 52 plus any desired safety margin foroverbalance, and starts the mud pumps.

As will be apparent from the foregoing description, the force bridges 76and 79 automatically computes and produces the signal which is amathematical function of the circulating pressure loss, and the relay 81automatically adds this signal to the signal proportional to the settingon dial 68 and subtracts 3 p.s.i. from the sum to produce a signal whichis proportional to the sum of the pressure Values represented.

This latter signal is then transmitted through the line 83 to the switchmeans including the valve casing 7() and switchable Valve member 71.With the Valve mem ber moved to the right, as shown in FIG. 3, thissignal is transmitted through lines 84 and 65 to the choke operator 40for urging the dow-restricting member toward maximum flow-restrictingposition. At the same time, a signal proportional to the standpipepressure is transmitted through line 51a, through valve 70, into line 72and then through line `66 to choke operator 40 for urging theow-restricting member away from maximum oW- line-restricting position.Thus, the Well is controlled through the drill string by maintaining abottom hole pressure equal to the sum of the hydrostatic head of the mudand the sum of static standpipe pressure and the selected pressure plusthat part of circulating pressure loss occurring in the annulus. Thecirculating pressure loss is constantly being computed, andautomatically compensates for changes in the mud circulating rate.

As drilling mud is circulated through the Well, the choke 32 willautomatically adjust for any deviation from the predetermined pressuredifferential so as to maintain the standpipe pressure at the levelrequired for maintaining the bottom hole pressure substantiallyconstant.

When the kick has been circulated out of the Well bore, level 67 ismoved to its lower, manifold control position, and the heavier mud iscirculated down through the drill string 26 to the bottom of the hole.The added mud `weight necessary in order to provide an adequatehydrostatic pressure when such mud has reached the bottom of the holehas, of course, been computed in the manner described and indicated on adial 99 on the console 50.

Movement of the lever 67 switches the valve member 71 to the left-handposition shown in FIG. 4. In this shifted position of the valve member,a signal proportional to manifold pressure is transmitted by line 55athrough the switch to line 72 and thus into the line 66. Thus, thissignal is transmitted to the choke operator 40 for urging theflow-restricting member away from maximum dow-restricting position. Atthe same time, a signal proportional to the static pressure which wasset on the dial 68 is transmitted through line 82 and the switchingValve into line 84 where it is transmitted by amplifier 85 and throughline 65 to the operator 40 of the choke. This latter signal urges theflow-restricting member toward maximum How-restricting position. Sinceit is a mathematical function of the Set static pressure, this signal isa constant so that the dow-restricting member of the choke 32automatically adjusts in such a manner that the opposing signal throughline 66, which is proportional to the manifold pressure, remainsconstant. This continues until the heavier mud is pumped to the bottomof the hole.

At this time, the user turns the knob 68a to change the reading on thestatic pressure dial 68 to zero, and moves the lever 67 to the upperposition of FIG. 2 for switching the system to drill string control.This, of course, switches the valve member 71 back to the right, asshown in FIG. 3. However, since the dial 68 for static pressure has beenmoved to zero, the sum which is transmitted from the relay 81 to thevalve 70 by means of line 83 is proportional only to the circulatingpressure loss, so that the signal transmitted to the operator 40 forurging the How-restricting member to flow-restricting position issimilarly a signal proportional only to the circulating pressure loss.This signal, of course, is opposed by a signal proportional to standpipepressure transmitted through line 51a and the switching valve into line72 to the operator 40 through line 66. Thus, during circulation of theheavier mud upwardly through the annulus of the well, the chokeautomatically adjusts to maintain the standpipe pressure at a levelequal to the computed circulating pressure. The user begins to weigh themud returns as soon as the manifold pressure indicated on dial 56 readszero. When the Weight of the returns approaches that of the heavier mud,the user checks the hole to see if it runs over with the mud pumpstopped. If it does not, he knows the well is killed.

In the event of a severe kick, or with expensive rig rates, the user maywant to start killing the well at the same time he starts to circulatethe kick out of the annulus. In doing so, he will reduce the amount ofpressure built up on the annulus, and also reduce the amount of time thedrill bit is inactive.

In this latter alternative method, he follows the same initial steps asin the other method above-described when he encounters a kickf That is,he picks the bit up off the bottom of the hole, he shuts the mud pumpsdown, and closes the preventer rams about the drill string. Furthermore,he reads and sets the static pressure in the standpipe upon the dial 68after the well has been shut in for a short time. Normally, he will addto this reading an overbalance and set the sum on the dial 68. Hefurther reads and records the choke manifold and standpipe pressures, asindicated on dial 56, moves the lever 67 to standpipe control position,and resumes mud circulation.

In this method, the user immediately begins to circulate the mud intothe drill string at whatever rate he is able to mix the mud. He readsthe dial 99 indicating mud weight increase and mixes his mudaccordingly, knowing that this reading includes any overbalance he hasadded to the static pressure. The user determines how long it takes thenew mud to get to the bit at the bottom of the drill string, and reducesthe static pressure gradually so that it reaches zero when the heaviermud arrives at the bit.

More particularly, as the heavier mud reaches the sensing device 61, theuser observes the change in circulating pressure loss reflected on thedial 60, and reduces the static pressure reading on the dial '68 acorresponding amount by suitable adjustment of the knob 68a. He thencontinues to adjust this knob in order to continuously reduce the staticpressure, as adjusted, in proportion to the depth reached by the mud,until such pressure reading is zero. He also watches the manifoldpressure dial 56, and when it reaches zero he knows that the well shouldbe dead. He then beings to weigh mud returns, and when they are within apoint or two of the heavier mud weight, he checks the hole to see if itwill run over. If it does not, he knows that the well is dead.

Other methods may be advisable under these same or different conditions,and the use of such methods with this system are contemplated by thepresent invention. Also, of course, the user may use this system indrilling under pressure, in which case he merely follows thoseprocedures described in accordance with the irst method during theinitial standpipe control of the well.

As shown in FIG. 5, in its preferred form, the choke 32 includes a body100 having a chamber 101 therein intersected by an inlet 102 to thechamber and an outlet 1103 from the chamber. The inlet and outlet areformed at right angles to one another and the intersection of the innerend of the outlet 103 with the chamber 101 forms an annular seat 104which is adapted to be substantially closed by an annular,flow-restricting member 105 which moves axially toward and away from theoutlet. Thus, in the position of the flow-restricting member shown inFIG. 5, there is an annular opening between the inner end of theow-restricting member and the inner end of the seat 104 through whichfluid may pass from the inlet 102 to the outlet 103. As the member 105moves to the left, this annular opening is, of course, enlarged so as topermit less restricted flow, in which case there is less back pressureon the annulus 29 of the well.

On the other hand, as the member 105 moves to the right, it furtherrestricts the annular opening between its inner end and the inner end ofseat 104, so as to thereby increase the back pressure in the annulus 29.In its extreme right-hand position, the inner end of member 105 moves ashort distance into the inner end of the seat 104 so as to restrict flowthrough the choke to a maximum extent.

The operator 40 comprises a T-shaped fitting 106 having its small endremovably mounted within an opening 107 in choke 100 to close same. Thisopening extends from the chamber to the outer end of the body in axialalignment with both the outlet 103 and the seat 104, and thus parallelto the direction of movement of member 105. Thus, in a manner to bedescribed hereafter, the

12 member is guidably slidable within the small end of tting 106.

The opposite large end of the fitting 106 comprises a cylinder 109formed between a cup-shaped opening covered by a plate 108 releasablysecured to and sealably engaged with the inside of the cup. A piston 110is sealably slidable within the cylinder for reciprocation along theaxis of reciprocation of the member 105, and a stem 111 extends throughthe tting to connect the piston to a head on the flowrestricting member105. Thus, reciprocation of the piston 110 of the operator will cause acorresponding reciprocation of the how-restricting member 105 betweenthe positions previously described.

This reciprocation of the piston results from the transmittal to itsopposite sides of the signals previously described in connection witheach of the systems. Thus, there is a threaded port 112 in the plate 108for connection with the line 65. Also, there is a port 112a through thecup for threaded connection with the line 66.

The stem 111 has a telltale 11111 extending sealably through the plate108 and of the same diameter as the portion thereof extending sealablythrough the fitting to connect piston 110 to flow-restricting member105. Thus, the piston 110 is balanced in this preferred embodiment ofthe choke 32, which is of advantage in responding to the signals. Thetelltale 111a is visible through a slotted guard 114 mounted about it onthe outer side of plate 108 to permit the user to determine, by itsmovement, whether or not the choke is working properly.

The small end of the fitting is received closely within choke bodyopening 107 and is sealed with respect thereto by a seal ring 116. Thisend of the iitting is hollow to provide a skirt 115 which extendsinwardly beyond opening 107 and into the chamber 101 to a position closeto the seat so as to support substantially the entire length of theflow-restricting member 105 which, as previously noted, fits closelywithin the inner diameter of the skirt 115 so as to be guided therebyduring its reciprocation.

As can be seen from FIG. 5, the flow-restricting member 105 is hollow atits inner end opposite the passageway 101, and has a head 116 on itsouter end for threaded connection to the end of the stem 111 of theoperator. There are a series of ports 11'7 extending through the head ofthe member 105 to freely connect the hollow interior of the member 105,and thus the chamber 101, with the area between the head and the closedend of the fitting at the base of the skirt 115. In this way, pressurewithin the choke 32 acts only over the cross sectional area of the stem1:11 to urge the flow-restricting member 105 to the left or away fromflow-restricting position. Even this small force is opposed by a forcedue t0 atmospheric pressure acting on the cross sectional area of thetelltale 11111, which, as previously mentioned, is of the same crosssectional area as the stem 111. Thus, there is a minimum of tendency forpressure within the choke to urge the'member 105 awayfrom-liow-restriction position, particularly due to pressure withinoutlet 103 when the member 105 is in its extreme position within seat104.

As can be seen from FIG. v5, the seat 104 comprises a removable ringwhich is cylindrical so as to be reversible end-for-end within anenlarged diameter portion 103:1 of the outlet 103 of the choke. Thus, itis possible to increase the life of the seat by so reversing it whenwear has taken place at the inner diameter of one end. The innerdiameter of each end of the seat ring is chamfered to facilitatemovement of the How-restricting member 105 into its extremeflow-restricting position. A seal ring 1.18 is received about a centralportion of the outer diameter of the ring so as to sealably engage withthe recessed portion 103:1 in either end-for-end position of the ring.

The hollow portion of flow-restricting member 105 is recessed about itsopen end to receive a removable sleeve 119, which is also cylindrical soas to be reversible end-for-end, similarly to the seat ring 104, on thehollow portion of such member. More particularly, the sleeve 119 forms acontinuation of the outer diameter of the hollow portion of thenow-restricting member so as to slide with it closely within the skirt115. The opposite ends of the outer diameter of the sleeve are chamferedfor guiding into the oppositely facing end of the ring 104.

A snap ring 120 is carried within the oppositely facing grooves on theinner diameter of the ring 119 and outer diameter of the recessedportion of the member 105 so as to releasably retain the sleeve aboutsuch member body. Access is had to the snap ring 120 by means of a slot121 extending from the end of the recessed portion of the member toaccommodate a tool of any suitable type. By means of this tool, the ringmay be held in a collapsed position to permit insertion and removal ofthe sleeve 119.

The inner corners of the seat 104 and the outer corners of the sleeve119' are lined with a hard, wear-resistant material, preferably tungstencarbide. More particularly, each such annular lining extends from anintermediate point on each of the seat ring or sleeve to an intermediatepoint on the inner and outer diameter thereof, respectively. Thus, thelinings cover the portions of these parts which are most susceptible ofwear. Furthermore, since the linings are over both corners of theseparts, they serve this function regardless of how they are disposedend-for-end.

The small end of the fitting 106, including the annular skirt 115thereof, is releasably mounted within the opening 107 of the choke bodyby means of snap ring 122 engaging in a groove in an outer end ofopening 107. Thus, an annular shoulder about the small end of thefitting is positioned to be opposite the inner side of this groove whensuch end is inserted fully within the choke body opening and seal ring116 is sealably engaged with such opening. As can be seen from FIG. 5,cover 108 is similarly releasably secured to the cupshaped open end ofthe fitting. As can also be seen from FIG. 5, suitable seals areprovided about the openings in plate 108 and the small end of thefitting 106 so as to seal about the stern 111 connecting to theflow-restricting member 105.

As will be apparent from the foregoing, upon removal of the small end ofthe tting from within opening 107, the seat ring 104 can be replaced orreversed end-for-end therethrough. Also, of course, with the fittingremoved, the sleeve 119 may also be replaced, or reversed endfor-end.

As previously described, and as shown in FIGS. 6 and 7, the sensingdevice 61 comprises a tubular conduit 125 of the same inner diameter asthe standpipe 28 and having means, such as anges, on its opposite endsfor connection in the standpipe as a smooth continuation thereof. Italso includes a shaft 126 extending diametrically through the oppositesides of 4the conduit for rotation therein, and an arm 127 mounted onthe shaft within the conduit for rotation therewith and extensionlongitudinally of the conduit'. There is a sensing element 128 in theshape of an airfoil or hydrofoil on the end of the arm 127 remote fromthe shaft 126 and occupying, in a neutral position, substantially themidportion of the conduit. More particularly, the sensing element 128 isarranged to be urged up or down out of the neutral position inproportion to the product of mud density times the square of the mudcirculation rate through the conduit.

In order to reduce turbulence within the sensing device to a minimum,the arm 127 is of at, narrow construction, as seen along the plane shownin FIG. 6, and of convergent tapering construction from the shaft 126 tothe sensing element 128, as seen in the plane of FIG. 7. Moreparticularly, the end of the arm 127 which surrounds the shaft 126includes a tear-drop portion 127a extending from one side to another ofthe conduit, as

14 shown in FIG. 6, and secured to the shaft 126 by means of a' setscrew 131.

As shown in FIG. 6, there is also an arm 129 mounted on one outer end ofthe shaft 126 for rotation therewith along the outer side of the conduit125. The end of this exterior arm 129 remote from the shaft 126 has ahead 130 thereon for engagement at its lower end with an oppositelyfacing part on the transmitter 62 which, as previously described, is ofsuch construction as to transmit a signal through line `63 proportionalto the force by which the flowing drilling mud urges the sensing element128 out of its neutral position. This force is, of course, transmittedto the head 130 through the arm 127, shaft 126, and arm 129.

The transmitter 62 is of a so-called null balance type which is operableto return the head 130 and thus the arm 129 to its original positionwith a force proportional to the signal which it transmits. A suitabledevice for this purpose is a Nullmatic Force Transmitter manufactured byMoore Products, Inc. Thus, in the operation of the sensing device 61,the flowing mud acts upon the element 129 to urge it out of the neutralposition shown in FIG. 7 with a force proportional to the product of themud density times the square of its circulating rate. This in turn istransmitted through the inner and outer arms to the transmitter `62,which in turn transmits a signal to the above-described product to theconsole 50.

As shown in FIG. 6, the opposite ends of the shaft 126 extend throughopenings 132 in sleeves 133 on opposite exterior sides of conduit 125.The inner end of each opening 132 has a shoulder 134 against which aseal ring 135 is held by means of a ball bearing 136. The bearing is inturn held tightly against the seal ring by means of a gland nut 137threadedly engaged with the outer threaded end of opening 132.Preferably, the seal ring 135 includes a thin disc of Teflon whose innerdiameter is held tightly against the outer diameter of the shaft 126. Bymeans of the gland nut 137 engaging against bearing 136, only the outerdiameter of the Teflon ring is held against rotation, so that its innerdiameter is free to rotate with the shaft 126 as the sensing element 128moves in a small arc responsive to the drilling mud ow. Thus, there is aminimum of frictional resistance to the rotation of the shaft 126, evenduring its small arc of rotation.

The transmitter 62 is releasably mounted upon a platform 138 suspendedfrom the lower side of the conduit 125, as seen in FIG. 7.

From the foregoing, it will be seen that this invention is one welladapted to attain all of the ends and objects hereinabove set forth,together with other advantages which are obvious and which are inherentto the apparatus and method.

It will be understood that certain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations.

As many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth or shown in the accompanying drawings is to beinterpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed 1. A sensingdevice, comprising a conduit for connection in a ilowline, a rotatableshaft extending within and through the side of the conduit, an armmounted on the shaft within the conduit for rotation therewith andextending longitudinally of the conduit, a sensing element mounted andarranged on the end of the arm remote from the shaft for swinging out ofa neutral position and thereby causing rotation of the arm and the shaftin proportion to MVZ, wherein M equals the density and V the velocity ofa uid flowing through the conduit, and means including a transmitter onthe exterior of the conduit responsive to rotation of the arm forreturning the sensing element to its neutral position, said transmitterhaving means for producing a signal which is a mathematical function ofthe force necessary to so return the sensing element.

2. A sensing device of the character described in claim 1, wherein saidreturning means includes an arm mounted on the shaft for rotationtherewith exteriorly of the conduit, said arm has a transmitteractuating part on the end thereof remote from the shaft, and saidtransmitter is of a null balance type and supported with a signal 15/1968 Gelinas 73-228 12/1959' Morse 73-228 RICHARD C. QUEISSER, PrimaryExaminer 0 M. SMOLLAR, Assistant Examiner U.S. C1. X.R.

